The present invention relates to telecommunication networks, data communication networks and broadcasting networks in general, and to access networks in particular.
An access network may in broad terms be defined as the means by which services of a network are made available to a terminal which is connected to the access network. The access system in its turn is connected to service provided network. In PSTN, for example, the access system comprises the network formed by the subscriber lines and equipment connected at each end of the individual subscriber lines; such as telephones at the subscriber side and terminal units at the local office side.
In this document an access system is defined as the means by which the services of an entity are made available to another entity at a certain point, the service access point (SAP) and enabling users to exploit the services. In this paper, an access system is an arrangement, separate from the accessed entities, which makes the services of one or several communication networks, and/or of one or several broadcasting networks, exploitable to a set of users. Thus, an access system provides a set of service access points to a number of different service providing networks.
Access systems are used to distribute the service access points of a set of service providing networks to locations, which are suitable for the users of the services of the networks.
Dedicated Accesses
Traditionally, telecommunication services have been provided by vertically integrated networks. The designers of the network and its components and protocols have used the knowledge of which services it would provide, and of the contexts, in which these services were to be provided. E.g., a PSTN is designed to provide point to point two-way connections, aimed to support 3.1 kHz speech. The networks were not designed for other services and contexts. This results in network components that fit together like pieces of a jigsaw puzzle. Such pieces are hard to reuse for other purposes, or for a new contexts.
Also the access arrangements are integrated in the same way. E.g., the access network of PSTN is simply seen as an extension of the PSTN. It is assumed that each terminal is connected over a dedicated pair of copper wires, and at least some of the control signaling is performed by opening and/or closing the loop. There is no need to have a separate address domain in the access network, since each service access point has its own dedicated copper line.
The integration of access arrangement and network goes so far that it is possible to classify vertically integrated networks by their access type; that is access protocoll, kind of terminal used for the access and services provided by the service providing network. Sometimes the terminal itself makes it possible to identify the service network. A telex apparatus for example is dedicated to the telex service of the telex network. Likewise a telephone set is dedicated to a telephony network; it cannot be used in any other type of network. An mobile telephone set gives access to the mobile telephony service, it cannot be used in the PSTN because its access protocol is different from the PSTN access protocols.
Besides the analogue access to PSTN, there are e.g. X.25 and X.21, which are dedicated access protocols interfacing specialized networks.
The recent development of access networks to PSTN and ISDN, e.g. the V5 standards, follows the same line. The access arrangement is dedicated for the services of PSTN and ISDN. It is also assumed that the owner of the access network is the same as the owner of the accessed network. The possibility to access more than one network of the same kind, but with different ownership, seems not to be covered.
If we look at mobile telephone networks, there are a number of different analogue and digital access types. Dedicated terminals are required for each type of network and are incompatible with other networks. The different networks provides basically the same type of service. From the above it is obvious, that an access is dedicated to a combination of network and service, not to a service only.
Integrated Services Networks
For a long time, new techniques have been developed in order to increase the transmission capabilities of traditional access infrastructure. An example of this is DSL (Digital Subscriber Line), which is the transmission protocol for ISDN access, which provides a 144 kb/s transmission link over a traditional copper subscriber line. Other modulation techniques, xDSL, are already specified, or are under specification, which gives symmetrical or asymmetrical rates up to several Mb/s over a copper wire.
During the last couple of decades, a number of network concepts have been proposed like ISDN and B-ISDN. They aim to provide a number of services, which traditionally have been provided by different networks, by a single network with its own address domain.
Also in these cases, a dedicated access approach is taken. E.g., for ISDN (Integrated Services Digital Network), services like telephony, which were accessed in one way when they were provided by the legacy networks, are accessed in a quite different way over the integrated ISDN access. The way a user accesses the services of these networks is still dedicated, but the range of services is wider, and it is easier to add new services. We call this type of access to an integrated service network an integrated access. In ISDN Network Terminals (NT) are used, which connects to a number of terminals. Simple NTs just conveys the access protocols to the terminals, but more complicated NTs exists, e.g. with a functionality like a traditional Private Branch Exchange (PABX).
The integrated networks were defined as a single, homogeneous network with its own, specific interfaces, even towards the terminals. When new services are required, new capabilities have to be integrated in the integrated networks. New services are traditionally added following the three step method. In the first step the new service is described in an implementation independent manner. In the second step the units required to support the new service and to be added to the nework are defined. The units are sorted in functional groups which then are distributed to physical units. The third step is to design protocols in the integrated network. This latter step means that the integrated network is essentially service specific. Possibly, but not necessarily, new capabilities need to be integrated also in the terminals when new services are added to an integrated network.
When the integrated service networks were defined, migration issues were not focused. There are at least two aspects of migration. The first one is the relation between legacy networks (i.e. the existing networks, which do not confirm to the new one) and new networks. The other is the relation between users (and the equipment of users) and the services, which used to be provided in one way by a legacy network, but which now can be provided in another way over an integrated access of an integrated services network.
The second relation is basically that the user has to change terminals and other communications equipment, and in most cases also their address (such as telephone number), if they decide to connect to a network of this kind. There is sometimes a possibility to reuse the terminals by adding an adapter, which adapts to the interfaces of the integrated access.
The first type of migration is handled in the following way. The legacy networks are seen as something, which breaks the homogeneity of the integrated network, and is dealt with by Interworking Functions, which map the services of the legacy networks on the services of the integrated network as good as possible. In this way, the connectivity (i.e. the addressable destinations and the information transfer services, which can operate between them) of the new network can be extended to the legacy networks. This may include address conversions between different address domains (e.g. between IP addresses of Internet and E. 164 addresses of PSTN), or it may require the capability to handle addresses of other address plans. The latter is the case e.g. when an ISDN destination (E. 164 address) is called from a PSDN (Public Switched Data Network), which handles addresses according to the X. 121 address plan.
The common understanding of the administrative relationships concerning integrated accesses is that they, like in the case of the dedicated accesses, are extensions of the network, and owned by the network operator.
DATA COMMUNICATION
The control structure of traditional data communication, e.g. Public Switched Packet Data Networks (PSPDN) using X.25 as the main access protocol, is organized in much the same way as PSTN. X.25 supports connection oriented communication services. The access protocols are layered, but essentially the access to an X.25 network is dedicated.
The OSI model (Open Systems Interconnect), aims to separate different concerns, and define an architecture for system interconnection, based on services of different layers, which are provided to client layers. OSI, however does not say anything about access to the services of a system.
The Internet concept, which also has an layered architecture, differs fundamentally from the integrated services network concepts, which originate in the telecommunications area. Internet is not vertically integrated, but provide an IP based connectivity network, which can be used by any application. IP networks provides a connection-less service. IP-based networks do only provide connectivity services. The types of xe2x80x9csupplementary servicesxe2x80x9d, which are frequent in vertically integrated networks, are lacking in IP based networks.
Access to an IP based network can be arranged by any link, permanent or semipermanent or dynamic (e.g. switched), which can transport IP packets. Such links are usually provided by separate agencies, e.g. a PSTN operator, or someone providing leased lines.
BROADCASTING NETWORKS
A third type of network are the broadcasting networks, which are mainly point-to-multi-point or point-to-any-point networks, distributing a number of TV and/or radio channels.
Often, broadcasting networks do not have addresses. Instead, terminals are connected to an ether, either an open ether, e.g. terrestrial or satellite TV broadcasting, or a closed ether, e.g. cable TV.
In order to confine the distribution of certain TV channels, e.g. in order to allow only paying users to view them, a set top box (STB) is used. An STB can be addressed, and managed in order to decode those the channels paid for.
Traditionally, broadcasting networks are analogue. However, the recent development of broadcasting networks includes the introduction of digital standards, e.g. Digital Video Broadcasting (DVB), and Digital Audio Broadcasting (DAB). Such networks can be used not only for broadcasting of radio or TV channels, but also for distributing other kind of information to several or a single destination.
OVERLAY ACCESS
A different type of access is using the transparent service of another network. In this case, the accessed entity lacks a complete access infrastructure of its own, i.e. its geographical coverage is incomplete. The users of the network are geographically distributed and for economic reasons the network does not cover the user sites. Instead the accessed entity is using the connectivity services of another network (an accessing network) to establish a link between the terminal belonging to the user and the service access point (SAP) of the accessed network. This is the overlay access concept. Entities in the terminal can then communicate with entities in the accessed network, and make the services of the network available to other entities in the terminal. In this way, the SAP of the accessed network can be distributed to all locations, which have access to the accessing network.
This kind of access is frequent for e.g. Internet, which is often accessed over a 28.8 kb/s modem connection to a modem pool of an Internet Service Provider. It is also frequent as an access method to Public Switched Packet Data Networks, standardized in the ITU-T recommendation X.28. It can also be used to access information services (e.g. Videotex services and Bank on Phone).
The overlay access concept is recursive and can be repeated more than once. Imagine a PC (personal computer) connected to the subscriber line via a modem and an Internet server with a modem pool connected to the PSTN. The PC can set up a modem connection to the modem pool via PSTN and access Internet via the Internet server. Over the IP network an application in the PC can reach a voice gateway enabling access to ISDN/PSTN. This is an example of recursiveness of the overlay access concept.
No requirements are made on the ownership of the different access networks. They can of course have another owner than the accessed network.
GENERAL RADIO ACCESS NETWORK
Applicant""s PCT/SE96/00510 relates to a radio based access network supporting terminal mobility, and accessing various networks. Terminals are communicating with their service network with the same signaling protocols as ordinary terminals of these networks uses. In case of terminals lacking radio interfaces, they can be connected to a terminal adapter, which has a radio interface. The signaling is conveyed transparent by the general access network.
This preference differs from what is proposed in the present invention in a number of ways. There is a lack of adaption units, and the services of the accessed networks are transparently passed to the connected terminals. Further, the quoted document is restricted to radio access networks. The protocols of the service networks are terminated by the terminals. The service protocols of all service networks have to be terminated in the terminal. This means that the terminal has to be dedicated to all service networks that is supposed to be reached.
IP BASED ACCESS NETWORKS
Applicant""s recently filed patent applications, PCT/SE97/00968, PCT/SE 97/00969 and PCT/SE97/00970 relate to access arrangement using IP as an internal connectivity protocol. The main idea is to give a user access to at least one telephony network, and at least one IP based network, over a common access network. The main components of these applications are adaption units, called network terminals (NT), which can have one or more telephone interfaces (e.g. analogue), and one or more interfaces to computers. Service access points to at least one telephony network and at least one IP based networks are distributed to the NT by the means of the connectivity services of an IP network. An IP link is carried by any suitable transmission technology, e.g. a switched modem connection, or by a copper access line enhanced with a xDSL modem, or an optical fibre or by a CATV network. The access protocols to the accessed networks terminate in other adaption units, named router and telephony gateway, and more general service specific protocols are exchanging service specific control information between the adaptation units. The inventions are based on IP as connectivity technology only, and treats only access to PSTN/ISDN networks and IP networks. The only terminals treated are phones and PC:s.
One object of the present invention is to provide access to a multitude of service providing networks of the same type as well as of several different types by means of a common access system. It is also an object of the present invention to provide for an easy adaptation of the available services to individual requests of different users. Another object of the present invention is to provide an access system which is able to access new service providing networks, presenting new services and/or new access protocols, with minimal impact on the access system. A further object of the present invention is to provide an access system which enables the user domain to develop independent of the access network and the service providing networks. Furthermore, the present invention should offer a possibility to use any terminal or combination of terminals for any service, provided that the capabilities of the terminals are sufficient. Yet another object of the present invention is to provide an access system which may use any transmission technique or combination thereof without affecting the implementation of the rest of the access system, providing for the possibility of performing smooth migrations concerning transmission technique. Still another object of the present invention is to provide an access system which may use any suitable connectivity technique or combination thereof without affecting the implementation of the rest of the access system. All the above mentioned objects should be provided by an access system.
The above objects are achieved by a general access system according to the appended claims.
The general access system according to the present invention comprises a connectivity network, at least one access adapter, to which at least one service providing network is connected, and at least one network terminal, to which at least one terminal is connected. The access adapters terminate the access protocols of the service providing networks. The access system distributes the service access points of the service providing networks transparently over the connectivity network to network terminals. The general access system according to the present invention separates different concerns; the different concerns of service providing networks as well as the user equipment are separated from the concerns of the connectivity and transmission aspects of the access arrangements. The access network is transparent to the accessed services. Furthermore, in a preferred embodiment of a network terminal according to the present invention, applications are provided, which are able to connect the distributed service access points of the service providing networks with at least one virtual terminal exhibiting appropriate devices.